In order to drive a display panel to display, gate lines of the display panel need to be sequentially scanned so as to turn on thin film transistors whose gates are connected to the respective gate lines. For a thin film transistor of any type, it is turned on when its gate voltage is within a turn-on voltage range thereof, and is turned off when its gate voltage is within a turn-off voltage range thereof.
Taking a P-type thin film transistor in a liquid crystal display apparatus as an example, a turn-on voltage of the P-type thin film transistor is in the range of about 12V to about 35V, and a turn-off voltage of the P-type thin film transistor is in the range of about −6V to about −15V. The turn-on voltage and the turn-off voltage are provided by a shift register connected to the gate lines, and the shift register unit is connected to an external power supply proving the foregoing voltages. However, an external voltage generally ranges from 2.5V to 3.3V, which is far from meeting the requirement of turning on and turning off a TFT.
Therefore, how to ensure voltages supplied to gate lines being capable of turning on or turning off thin film transistors becomes a technical problem to be solved urgently in the art.